This is a revised application. Multiple sclerosis s (MS) is caused by an uncontrolled immune response against self-antigens in the central nervous system: The autoreactive components in the immune system are usually controlled by regulatory T cells (Treg). Not surprisingly, deficits in the Treg compartment are associated to MS and the susceptibility of mice to develop experimental autoimmune encephalomyelitis (EAE), an experimental model of MS. Thus, the study of the molecular mechanisms controlling Treg function is needed to understand MS pathology and identify new therapeutic targets;these studies, however, cannot be easily performed in mammals. Worms and flies have been useful in the identification of the mechanisms governing innate immunity, but invertebrates do not have Treg. We found that the zebrafish has an immune system that shares several features with its mammalian counterpart, including the genes driving Treg differentiation. In this application we will use mice and zebrafish to identify the molecular pathways that control Treg generation. This goal will be achieved by three independent approaches: 1. Bioinformatic identification of transcription factors controlling Treg differentiation. 2. High throughput screen to identify chemicals that regulate Treg differentiation. 3. Characterization of the role of the transcription factors and chemical compounds on Treg activate during the course of EAE. This project has the potential to identify therapeutic targets for the management of MS, and to establish the zebrafish as a platform for the high throughput identification of immunomodulatory drugs. In summary, this is an innovative project that will combine the experimental advantages offered by mice and zebrafish to identify pathways controlling Treg generation and is consistent with the aims o f the New Pathway to Independence Award Program. RELEVANCE: Multiple sclerosis (MS) results from an attack of the immune system to the central nervous system (CNS). Under normal circumstances, the autoreactive components of the immune system are controlled by a specialized class of T cells termed regulatory T cells (Treg), but Treg are dysfunctional in MS patients and also in its experimental mouse model experimental autoimmune encephalomyelitis (EAE). In this project we will characterize metabolic pathways and compounds that control Treg biology, which might lead to novel pharmacologic interventions for MS.